Whomp's Fortress' Location
So in Super Mario Galaxy 2 Mario enters a Galaxy Called Throwback Galaxy which contains Whomp's Fortress. We know this is the same one from Super Mario 64 for several reasons.
The title of the mission is "Return of the Whom King." This is telling us this is not the first time Mario has faced off against King Whomp. The first time being in SM64.
The second reason is a Bob-omb Buddy recognizes Mario saying, "you look sorta familiar, 'stache man! How are you doing?"
The name of the Galaxy being Throwback or Nostalgia Galaxy is probably a nod to it being from SM64. Things like the 64 Outfit is described in universe as nostalgic for example.
So turns out the paintings of SM64 can even take people to far off Galaxies, and not just other places in the Mario World.
